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Mystery return air duct

In the process of fixing the ceilingfrom a leak upstairs we discovered a HUGE return unfinished air vent that was open and  just sucking in air from between the rafters.  We moved in the house new so I know it wasn't done after the fact.  This also explains why the house may be so dusty all the time and has never cooled off properly.  At any rate can anyone think of a legitimate reason for them doing this??



Re: Mystery return air duct





Return air ducts balance airflow in your HVAC system — The primary role of return ducts is to bring air that has been warmed or cooled back to your furnace or air conditioner. This air is returned so that it can be heated or cooled again, filtered of particulates and contaminants, and redistributed inside your home. This air circulation system must be balanced to ensure there is enough air entering and leaving to allow for proper HVAC equipment operation and consistent indoor temperatures.


Return air ducts must be correctly sized — The physical dimensions of return air ducts are important since they must be big enough to carry enough air back to your HVAC unit. If they are too small, airflow will be restricted and there will not be enough air circulation to heat or cool the inside of your home.


Return air ducts must be sealed and unobstructed — Sealing return air ducts is just as important as sealing supply ducts. Sealing all duct section connections with mastic, a specialized rubbery sealant, or with metal tape prevents air leaks. It also keeps additional particulates and other contaminants from being pulled into the ductwork system and sent out into your home. Remember, too, that return air ducts must be kept clear of obstructions at the grilles, including furniture, boxes, clothing, or other objects that would block airflow.


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